1. Field of the Invention
The present invention relates generally to mail sorting machinery and, more specifically, to adjustably pulleys for use in a mail induction subsystem which delivers mail to a transport/stacker module of a mail sorting system.
2. Description of the Related Art
A mail induction subsystem delivers pieces of mail individually to a transport/stacker module. The induction subsystem can include a number of separate modules, which collectively define a continuous delivery line for delivering mail to the transport/stacker module.
Each module of the induction subsystem may include one or more pulley assemblies which carry vertically oriented conveyor belts.
In order to accommodate mail pieces of variable width, the assignee of the present invention, Westinghouse Electric Corporation, has developed an induction subsystem which uses dancer pulleys in each pulley assembly of the induction subsystem to allow radially outward deflection of the pulleys, thus permitting wider pieces of mail to pass through counter-rotating vertical belts. The assignee's co-pending application, entitled "Induction Subsystem for Mail Sorting System" by Wakamiya et al., filed on Aug. 9, 1991, is incorporated herein by reference. Generally, as described in the aforementioned patent application, and as herein illustrated in FIG. 1 and 2, an induction line pulley assembly 32 includes a plurality of dancer pulleys 34, 36, 38, 40 and 42 which swing about respective axes 34a, 36a, 38a, 40a and 42a through a range of about 20.degree. . A belt 44 runs over the surface of the dancer pulleys and is looped around two end pulleys 46 and 48 which have rotation axes coplanar with the rotation axes of the dancer pulleys when the dancer pulleys are in the normal position. The belt 44 is driven by a drive pulley 52, and an idler pulley 56 ensures at least 180.degree. wrap of the belt 44 on the drive pulley 52. Also, the location of the idler pulley 56 is such that the belt geometry at the end pulley 48 is substantially the same as the end pulley 46.
A counter-rotating belt 58 runs between end pulleys 60 and 62, of which pulley 60 is driven, with idler pulley 64, 66, 68, 70 and 72 therebetween. Preferably, drive pulleys 52 and 60 are driven in opposite directions by a common drive belt which runs from a drive motor so that the belts 44 and 58 rotate at the same speed but in opposite directions.
Each dancer pulley is supported on a corresponding swing arm 74, 76, 78, 80 and 82, respectively, each of which is pivotally mounted to a horizontal plate 84. The plate 84 may be a countertop of a modular cabinet, for example, and has arcuate channels 86 formed therein to permit the dancer pulleys to swing arcuately away from the initial position wherein the pivot axes of the dancer pulleys are aligned with the pivot axes of the pulleys 46 and 48. The pivot axes of the pulleys 46 and 48 are fixed, while the pivot axes of the dancer pulleys swing radially outwardly away from the mail passage slot formed between the two belts 44 and 58.
The end dancer pulleys 34 and 42 are also supported at the upper ends by having a cam follower 88 ride in an arcuate cam track 90 formed in an upper support bar 92. The support bar is mounted on fixed pillar supports 94, 96, 98, 100 and 102.
The pulleys 62, 64, 66, 68, 70, 72 and 60 have fixed rotational axes, while the rotational axes of the dancer pulleys, as previously mentioned, swing outwardly to expand the distance between the inner run of belt 44 and the inner run of belt 58 to accommodate mail pieces of variable thickness. When the mail piece 50 pushes the dancer pulleys outwardly, a spring bias is generated by the belt 44 which causes the dancer pulleys to return to their original positions after the mail piece 50 has passed therethrough.
In order to keep the belts 44 and 58 properly positioned on their respective pulleys, the pulleys are crowned so as to help center the belts on the pulleys. Generally speaking, if the end dancer pulleys 34 and 42 are perfectly vertical, the belt 44 should ride centered on the pulleys. However, due to the fact that the rotational axis for each of the pulleys 34 and 42 varies positionally along an arc, and since the contact between the ca tracks 90 and 91 and the cam followers 88 is not fixed, some tilting of the pivot axes for the two rollers 34 and 42 may be encountered.
Another problem associated with the drive belts which operate under the countertop is that it is difficult to remove and install the drive belts, which also run on crowned pulleys, due to the fixed rotational axes of the belt pulleys.